1. Field of the Invention
The present invention relates to a method and apparatus for vibration detection and vibration analysis, a lithographic apparatus comprising such an apparatus, a device manufacturing method comprising such a method, and a computer program product comprising such a method.
2. Description of Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction), while synchronously scanning the substrate parallel or anti-parallel to this direction.
During exposure of a die, the image of the desired pattern is typically disturbed by a number of sources, for example, vibrations of the projection lens, temperature fluctuations of the ambient along the optical path, vibrations of the framework which encompasses the metrology devices, vibrations of other components and by measurement errors of interferometers for positioning a stage holding the substrate.
Due to the vibration of the image during exposure, a loss of contrast in the image may occur. The loss of contrast will result in reduced accuracy of alignment and of dimensions of (portions of) the imaged pattern. Since the accuracy of alignment is within a few tens of nanometers, the possible occurrence of vibrations with an amplitude of a same order of magnitude may have a strong impact on the image quality. Clearly, vibrations should be minimal.